Photographic sound recording



July 6, 1943 E. w. KELLOGG PHOTOGRAPHIC SOUND RECORDING Filed June 30, 1941 I 3nventor Q Gttorneg Patented July 6, 1943 PHOTOGBAPHIC SOUND RECORDING Edward W. Kellogg, Indianapolis, Ind., assignor to Radio Corporation of America, a corporation of Delaware Application June 30, 1941, Serial No. 400,541

3 Claims.

This invention relates to a sound recording optical system for making variable density sound records by the use of a galvanometer. Heretoi'ore there have been a number of methods in use tor making variable density sound records, such as the glow-lamp system, the light valve and the penumbra system. Of these only the penumbra system uses a galvanometer.

The use of a galvanometer is desirable since it avoids the ribbon velocity distortion which is characteristic of light valve recording. The present system has the advantage over the penumbra system that only a very narrow mirror is required, thereby reducing inertia effects. A uniform light intensity is used instead of a pcnumbra and the beam of light is moved to a greater or less extent across an aperture stop in the optical system which determines the quantity of light transmitted to the film.

Une object of the invention is to provide an impmved sound recording optical system of" the variabledensity type.

ltnothcr object of the invention is to provide a variable density sound recording optical system using a galvanometer to modulate the light transmitted.

another object of the invention is to provide a sound recording optical system which is capable extremely accurate adjustment and calibre tlo'n.

Uther and incidental objects of the invention will apparent to those skilled in the art from reading or the following specification and an inspection of the accompanying drawing in which: V

Figure is a perspective view or my improved optical systems, the various casings being removed,

Figure elevation of an alternative type of aperture which may be used in the apparatus.

Referring first to Fig. 1, light from the source it is directed through the condenser lens it and past the fixed stop it. This stop preferably has a straight edge and is shown as reaching approxicity to the optical axis of the system. Light sing stop it is directed by the lens l 3 upon galvanometer mirror it, the light source it imaged upon the mirror it by the lenses hi it reflected by the mirror it passes through the slit iii toward the aperture plate ll. If a narrow filament is used in the lamp it or ii a very narrow galvanometer mirror is used at N, slit it may be omitted, if desired. but the slit advantageous in reducing stray light.

till

The narrow aperture or slit which determines the width of the line of light focused on the film. is located close to the galvanometer mirror, as shown at IS in Fig. 1. In the vertical plane this is imaged on the film by lenses I9 and 21, the cylindrical lenses l6 and I8 having no efiect in this plane.

The light passing through the slit I5 is directed onto the aperture H by the cylindrical condenser lens IS, the purpose of which is to insure illumination of the entire length of the linear image on the film F. In the horizontal plane the light paths are essentially the same as in the usual galvanometer type recording systems in which a narrow slit is located at I1 and a condensing lens at it. Thus, the width of aperture H which is focused on the film by the combined action of lenses l8, l9 and 2|, determines the width of the exposed area on the film. The vertical axis cylinder I8 is needed to bring aperture l1 into focus on the film in the horizontal plane, since the spherical lenses l9 and 2! are only strong enough by themselves to image aperture IS on the film.

Lens i9 in conjunction with the lens l3 forms an image of the stop it in the plane of the aperture in the plate 20, and this image is moved up and down across the aperture in the plate 20 by the galvanometer it, thereby varying the effective aperture with which the film is exposed or in other. words varying the quantity of illumination.

transmitted through this aperture. The light passing through the aperture in the plate 20 is focused by the lens 2i upon the film F in the form of a narrow line extending transversely of the film. The lenses 2t and M in the vertical plane (or plane longitudinally of the film) form an image of the slit in the plate l5, or if this slit be omitted, of the galvanometer mirror or filament image therein. The width of the line of light is correspondingly small. since the image in this plane is unafiected by the cylindrical lens it and it.

The arrangement thus far described will produce a variation in illumination on the film I vanometer deflection. The shape or the aperture 20a is approximately that which would ordinarily be used to compensate for the curvature of the characteristic curve of the emulsion to be used plotted in terms of opacity versus exposure. The aperture Zia may, of course, be shaped as desired to comply with any other requirements as to corrections either in negative or printing characteristics or may be shaped to provide, in connection with a ground noise reduction system, volume expansion or com pression.

I claim as myinvention:

1. A sound recording optical system including in sequence, a light source, a condenser lens, a

- fixed stop defining a side of the light beam, lens means forming an image of said light source, means in the plane of said image for vibrating the beam in accordance with sounds to be recorded, a plate having a light slit therein, means for producing an image of said fixed stop, an aperture plate for receiving said image, and an objective for directing said beam of light in the form of a fine line image of said light slit upon a film, said aperture plate being located in an aperture stop plane of said objective.

2. A sound recording optical system including a light source, a condenser lens, a fixed stop defining a side of the light beam, lens means iorminganimageotsaidlightsourcameans intheplaneotsaidhnageforvibratingthebeam .inaccordancewithsoundgtobereoordeda plate having a light slit therein, means for producing an image of said fixed stop, an aperture plate for receiving said image, an aperture plate between said slit and said receivingaperture plate, and an objective for directing said beam of'light in the form of a fine line image of said light slit having its ends defined by said inter? mediate aperture plate.

3. A sound recording optical system including a light source, a condenser lens,'a fixed stop defining a side oi.' the light beam, lens means forming an image of said light source, means in the plane of said image for vibrating the beam in accordance with sounds to be recorded, a plate having a light slit therein, means for producing an image of said fixed stop, an aperture plate for receiving said image having the aperture therein shaped to compensate for the characteristic curve of the photographic emulsion on which sounds are to be recorded, an aperture plate between said slit and said receiving aperture plate, and an objective for directing said beam of light in the form of a fine line image nnwsrm w. ELLOGG. 

